Following the progress of technology, cellular phone realizes a human desire of wireless communication and enables people to get rid of the constraint of corded phone. In addition to giving users more freedom, it shortens the distance between people.
However, when a radio signal being transmitted in space runs into obstacles, such as building, lake surface, glass, etc., certain phenomenon like reflection, refraction, diffraction, interference, etc. will happen that cause a signal to be received many times by a base station at different time. This kind of signal is called a multi-path signal. In addition to a deformation phenomena caused by jamming, multi-path signal exists a signal fading condition that it may be sometimes too fade to be recognized by base station. Therefore, the base station of the present invention employs rake receivers to receive multi-path signals in order to overcome the above problems.
Please refer to FIG. 1, which is a schematic diagram of the rake receiver 1 in a receiving system. As seen, a transmitted signal 10 received by an antenna 11 is transformed into an electrical signal by an input interface 12, then the signal passes through a filter 13, which is usually a band-pass filter, so as to filter out noises at high and low frequency, and afterward, it is sent to the processor 14 which might be a rake receiver. After transmitted signal 10 is radiated from a transmitting end, the signal is transmitted through multiple paths, and when it happen, different routing will have different arriving time. In timing fixer 15, delay estimation is implemented to find out several delay paths for multiple rake fingers. In phase fixer 16, phase rotation of signals is estimated to retrieve channel effect. Both timing fixer 15 and phase fixer 16 compensate the fading phenomenon. After processor 14 integrates all the received signals that has been corrected, a signal with better quality can be obtained. The signal with better quality further passes through a demodulation process of the decoder 17 and outputs therefrom a recovered signal for posterior circuit.
In the prior arts, a base station can be divided into several cells. Therefore, signals emitted by a user can be received not only by the cell where the user is located, but also by other cells. To improve quality of signal, it is also necessary to receive those signals with rake receiver 1. From aspect of the base station, a single user will require several sets of rake receiver 1 to receive signals correctly. However, when the signal quality is good enough, it causes waste of hardware. Please refer to FIG. 2, which is a diagram showing the rake receiver for base station according to the prior arts. As seen, a base station comprises a plurality of processing units 3 operating independently and a posterior circuit 8. The processing unit 3 further comprises a plurality of rake receivers 1, each can receiver a multi-path signal in its own circumstance which goes through a recovery process and outputs a recovered signal 19 therefrom; an combiner 2, which connects with the plurality of rake receivers and receives a plurality of recovered signals 19, then further integrates the plural recovered signals which are originated from a same source by an integration process and, consequently, outputs an integrated signal 29 therefrom to be used by a posterior circuit 8.
Take an example for detailed description that, when a user turns on its cellular phone, a preamble signal for initialization will be sent to a base station. The base station then, according to the preamble signal, assigns a processing unit 3 for receiving the preamble. For instance, when the environment is not good, five multi-path signals are generated accordingly. In order to have better efficiency, all five of the signals must be take into consideration simultaneously in the receiving end. Consequently, five rake receivers 1 are required for receiving signals, and a processing unit 3 capable of providing more than five rake receivers 1 is needed accordingly. However, in the prior art, each processing unit 3 is a hardware that does not support each other. That is, if every processing unit 3 contains more than five rake receivers 1, several idling rake receivers 1 will be wasted. On the other hand, if only five rake receivers 1 are installed while seven rake receivers 1 are needed actually for seven multi-path signals the efficiency of processing unit 3 will drop. Therefore, the number of rake receivers 1 within processing unit is a critical issue in design.
Moreover, in order to maintain a good communication quality, it is required to maintain a large amount of processing units in active state. In a long hour operation situation, processing unit is easy to malfunction and its lifespan is shorten, so that the cost of base station is increased. Hence, a new architecture is required to improve the above drawback.